Fog clearing from the turn basin as the morning sky turns blue. Source: National Aeronautics and Space Administration.
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Many negative emissions technologies are in early stages of experimentation, demonstration, or adoption. As such, it is difficult to fully assess their various performances, costs, and impacts. Technological development and policy priorities are critical to the success of NETs. Challenges can be overcome by more aggressively scaling up pilot efforts, promoting international agreements that accelerate mitigation, addressing the weakness of market forces to fund deployment of CCS and viable NETs, and allocating resources needed to meet the 2°C goal of the Paris Accord. This MIT Energy Initiative Podcast sheds additional light on negative emissions strategies and how they can be implemented at scale. 

One summary of viability, costs, and environmental considerations of known NETs today (EASAC, 2018).

Delay in deployment of conventional mitigation exacerbates the magnitude of the task as CO2 concentrations increase. Researchers caution against thinking of NETs as a safety net for the future, as this can drive rationalization of continued fossil fuel use in the present, and valuable time investing in alternatives may be lost (Smith et al. 2016). What if NETs don’t meet expectations on technical, economic or environmental criteria? The window for action is still open to achieve the Paris goal, but it requires massive reductions in greenhouse gases and wise land use practices that gain increasing traction from the present moving forward.